In the state of the art, it is known to use systems for marking moving objects, for example from Spanish patents n.sup.o 8901979 and n.sup.o 9602373 which describe a marking system using a laser which comprises a source of laser emission such as a CO.sub.2 laser of which the bean impinges on an acousto-optical deflector to which various frequency values are applied by means of a constant gain radiofrequency amplifier, to produce different angles of deflection of the laser beam impinging on the deflector, marking the character, logo, text, etc. This information to be printed is introduced into a data acquisition unit which generates a digitised N.times.M matrix of dots corresponding to the impression to be made and is saved in a memory.
The deflected beams are applied to the surface to be marked by means of optical focusing means of which the function is to focus the deflected laser beam on to the surface to be marked.
Although this type of system operates perfectly, it has the drawback that the CO.sub.2 laser tube has very large dimensions so it is difficult to site it in production lines.
A further drawback is that CO.sub.2 laser tubes are very expensive.
It should also be mentioned that this type of system has the drawback that it is necessary to include an acousto-optical deflector which, apart from its cost, does not have a very high power output owing to the losses by absorption and the low efficiency of deflection, due to the fact that it loses laser power by the mere fact of passing through the crystal of the deflector and, furthermore, a proportion of the resultant power cannot be deflected owing to the intrinsic limitations of acousto-optical deflection.
On the other hand, laser diodes are known of which a basic characteristic is that, from a very small size, they are capable of generating a laser beam with a considerable power level and with very low energy consumption.
At present, there is no marking system which employs laser diodes to produce the marking according to a N.times.M matrix of dots, which would be a system with a smaller volume and lower costs.